Conventionally, in an image forming apparatus, such as, e.g., a printer, a photocopier, a facsimile, and a multifunction machine (MFP), for example, a color printer using an electrophotographic system capable of performing special color printing, white, cyan, magenta, yellow, and black image forming units, LED heads arranged corresponding to the image forming units, a transfer unit, and a fuser part, etc., are arranged, toner images formed in the image forming units are transferred onto a sheet in an overlapped manner to form a color toner image, and the color toner image is fused to the sheet in a fuser part to form a color image.
In this type of printer, correction process, such as, e.g., a color shift correction and a density correction, is performed for all image forming units that are arranged (for example, see Patent Document 1).